K3 and later with updated firmware do the better azw3.
I think only the first two 6" Kindles, DX and DXG are limited to the very ancient mobi, which was obsolete before Amzon released any kindles (2007 and later). It was used by Mobipocket, which was bought by Amazon in 2005.
All Paperwhites, Touch, Basic, Voyage, Oasis do azw3 which works far better and is much closer to epub or docx. Mobi is related to HTML3!
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